The present invention relates to a control unit for a power steering apparatus of a hydraulic cylinder (steering cylinder) suitable for driving and controlling the steered wheels at a prescribed steering angle (hereinafter referred to as the tire angle, for the sake of convenience) in response to a rotational position of the steering wheel. The present invention also relates to a steering-wheel-angle correcting system for correcting deviation in the relation of correspondence between the steering wheel angle and the tire angle of the steered wheels corresponding to the rotational position of the steering wheel, more specifically a steering wheel angle correcting system suitable for vehicles with different steering wheel rotational ranges or steering ranges of steered wheels.
On industrial vehicles such as fork lift trucks, etc., there is provided a power steering apparatus to enable smooth steering wheel operation. As the power steering apparatus, a full-hydraulic power steering apparatus is known which is realized in a way to steer the steered wheels by feeding oil, in an amount corresponding to the amount of rotational operation of the steering wheel, to the steering cylinder by means of a hydraulic operating fluid feed unit.
In the above-described type of power steering apparatus, the amount of oil fed to the steering cylinder by the hydraulic fluid feed unit varies, in some cases, because of the rotating speed of the steering wheel. For example, in the case where the rotating speed of the steering wheel is comparatively slow, the amount of oil fed to the steering cylinder is liable to be reduced. In that case, a problem appears that a deviation is produced in the relation of correspondence between the steering wheel angle corresponding to the actual amount of rotational operation and the tire angle of the steered wheels. Moreover, there are cases where the oil to be fed to the steering cylinder by the hydraulic fluid feed unit, etc. leaks, and the same problem as above also appears in such a case.
For that reason, a general practice followed on power steering apparatus is to correct deviation in the relation of correspondence between the steering wheel angle corresponding to the amount of rotational operation and the tire angle of the steered wheels. This kind of power steering apparatus is now known, conventionally, and examples are provided in the Japanese Laid-open Patent Publication No. 10-181626 and the Japanese Laid-open Patent Publication No. 10-287258, etc. For example, in the apparatus indicated in the Japanese Laid-open Patent Publication No. 10-181626, the steering wheel angle corresponding to the amount of rotational operation is detected with a steering wheel angle sensor, and the steering angle of the steered wheels (tire angle) at that time is detected with a steering angle sensor. On the part of the controller, it determines the target steering wheel angle, which is the normal steering wheel angle, with a steering wheel angle adjusting map based on the steering angle of the steered wheels and, in case the deviation between the target steering wheel angle and the (actual) steering wheel angle exceeds the range of tolerance, the controller opens an electromagnetic switching valve. This makes it possible to circulate part of the oil volume to be fed from the steering control unit (xe2x80x9cSCUxe2x80x9d), which may be of the type sold commercially for many years by one of the assignees of the present invention under the trademark xe2x80x9cOrbitrolxe2x80x9d (a registered trademark of Eaton Corporation). The SCU comprises a hydraulic operating fluid feed unit, which feeds fluid to the steering cylinder, and reduces the proportion of fluctuation of the steering cylinder against the amount of rotating operation of the steering wheel, thus enabling idling of the steering wheel. Namely, an adjustment of steering wheel is achieved until the amount of deviation is kept in the range of tolerance with idling of the steering wheel.
On the conventional power steering apparatus, the steering angle sensor, SCU, electromagnetic switching valve, etc. are constructed as independent units. For that reason, it has been rather complicated and troublesome to handle those units which must be treated separately from one another. Moreover, on the above-described apparatus, in which a steering wheel angle adjusting map was prepared, based on the range of rotation of the steering wheel and the steering range of the steered wheels on the applicable vehicle, and was memorized in advance in the controller, there was a problem that the apparatus was applicable only to a single type of vehicle having the particular range of rotation of the steering wheel and the particular steering range of the steered wheels in common.
It is therefore an object of the present invention to provide a control unit for use with a power steering apparatus with improved operability. It is another object of the present invention to provide a steering wheel angle correcting system applicable to vehicles with different steering wheel rotational ranges or steering ranges of steered wheels.
In order to accomplish the above-mentioned objects, the present invention provides a control unit for use with a power steering apparatus including a hydraulic cylinder for controlling steerage of steered wheels in response to rotation of a steering wheel and a tire angle sensor for detecting the tire angle of the steered wheels, the control unit comprising: a main operating-oil supply device (the SCU), removably connected to a rotation shaft of the steering wheel, for supplying the hydraulic cylinder with an amount of oil corresponding to a rotated amount of the steering wheel; a correcting-oil supply device for, in response to a control signal, supplying correcting oil to correct operation of the hydraulic cylinder; a steering-wheel-angle detector, disposed around the rotation shaft of the steering wheel connected with the main operating-oil supply device, for detecting a steering wheel angle corresponding to a rotational position of the steering wheel; and a control circuit device for generating, on the basis of the steering wheel angle detected by said steering-wheel-angle detector and the tire angle detected by the tire angle sensor, a control signal to compensate for a discrepancy in the corresponding relationship between the steering wheel angle and the tire angles, and controlling the supply, by said correcting-oil supply device, of the correcting oil, wherein the steering-wheel-angle detector and the control circuit device are attached to a housing of the main operating-oil supply device so that the steering-wheel-angle detector and the control circuit device are provided as a one-piece unit with the main operating-oil supply device.
According to the present invention, it becomes possible to promote improvement of operability of the control unit, because the steering-wheel-angle detector and the control circuit device can be handled as a one-piece unit, together with the main operating-oil supply device, as the main component element.
In order to accomplish the other object above-mentioned, the present invention provides a steering-wheel-angle correcting system for use with a power steering apparatus including a hydraulic device for controlling steerage of steered wheels in response to rotation of a steering wheel, the steering-wheel-angle correcting system comprising: a first section that learns an entire steered range of the steered wheels on the basis of a tire angle detection signal indicative of a tire angle of the steered wheels; a second section that learns a rotational range of the steering wheel corresponding to the entire steered range of the steered wheels, on the basis of a steering-wheel-angle detection signal corresponding to a rotational position of the steered wheel; a third section that determines, on the basis of the learned entire steered range of the steered wheels and the learned rotational range of the steering wheel corresponding to the entire steered range of the steered wheels, first modifying data concerning a rightward steering direction of the steered wheels and second modifying data concerning a leftward steering direction of the steered wheels; and a fourth section that modifies at least one of a current tire angle detection signal and current steering-wheel-angle detection signal in accordance with the first or second modifying data corresponding to a current steering direction of the steered wheels, so as to correct the steerage of the steered wheels in accordance with a deviation between the tire angle detection signal and the steering-wheel-angle detection signal.
According to the steering-wheel-angle correcting system of the present invention, the system is realized in a way to learn the entire steered range of the steered wheels and the rotational range of the steering wheel corresponding to it, modify at least one of the current tire angle detection signal or the current steering wheel angle detection signal with either the first or the second modifying data corresponding to the current steering direction of the steered wheels, and modify steerage of the steered wheels, depending on the deviation between the tire angle detection signal and the steering wheel angle detection signal. It then becomes possible to apply the power steering apparatus having this system to vehicles with different steering wheel rotating ranges or steering ranges of steered wheels, and correct deviation in the relation of correspondence between the steering wheel angle and the tire angle of the steered wheels corresponding to the rotational position of the steering wheel.